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<title>Debugging with GDB: Define</title>

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<a name="Define"></a>
<div class="header">
<p>
Next: <a href="Hooks.html#Hooks" accesskey="n" rel="next">Hooks</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="User_002ddefined-Commands"></a>
<h4 class="subsection">23.1.1 User-defined Commands</h4>

<a name="index-user_002ddefined-command"></a>
<a name="index-arguments_002c-to-user_002ddefined-commands"></a>
<p>A <em>user-defined command</em> is a sequence of <small>GDB</small> commands to
which you assign a new name as a command.  This is done with the
<code>define</code> command.  User commands may accept up to 10 arguments
separated by whitespace.  Arguments are accessed within the user command
via <code>$arg0&hellip;$arg9</code>.  A trivial example:
</p>
<div class="smallexample">
<pre class="smallexample">define adder
  print $arg0 + $arg1 + $arg2
end
</pre></div>

<p>To execute the command use:
</p>
<div class="smallexample">
<pre class="smallexample">adder 1 2 3
</pre></div>

<p>This defines the command <code>adder</code>, which prints the sum of
its three arguments.  Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.
</p>
<a name="index-argument-count-in-user_002ddefined-commands"></a>
<a name="index-how-many-arguments-_0028user_002ddefined-commands_0029"></a>
<p>In addition, <code>$argc</code> may be used to find out how many arguments have
been passed.  This expands to a number in the range 0&hellip;10.
</p>
<div class="smallexample">
<pre class="smallexample">define adder
  if $argc == 2
    print $arg0 + $arg1
  end
  if $argc == 3
    print $arg0 + $arg1 + $arg2
  end
end
</pre></div>

<dl compact="compact">
<dd>
<a name="index-define"></a>
</dd>
<dt><code>define <var>commandname</var></code></dt>
<dd><p>Define a command named <var>commandname</var>.  If there is already a command
by that name, you are asked to confirm that you want to redefine it.
The argument <var>commandname</var> may be a bare command name consisting of letters,
numbers, dashes, and underscores.  It may also start with any predefined
prefix command.  For example, &lsquo;<samp>define target my-target</samp>&rsquo; creates
a user-defined &lsquo;<samp>target my-target</samp>&rsquo; command.
</p>
<p>The definition of the command is made up of other <small>GDB</small> command lines,
which are given following the <code>define</code> command.  The end of these
commands is marked by a line containing <code>end</code>.
</p>
<a name="index-document"></a>
<a name="index-end-_0028user_002ddefined-commands_0029"></a>
</dd>
<dt><code>document <var>commandname</var></code></dt>
<dd><p>Document the user-defined command <var>commandname</var>, so that it can be
accessed by <code>help</code>.  The command <var>commandname</var> must already be
defined.  This command reads lines of documentation just as <code>define</code>
reads the lines of the command definition, ending with <code>end</code>.
After the <code>document</code> command is finished, <code>help</code> on command
<var>commandname</var> displays the documentation you have written.
</p>
<p>You may use the <code>document</code> command again to change the
documentation of a command.  Redefining the command with <code>define</code>
does not change the documentation.
</p>
<a name="index-dont_002drepeat-1"></a>
<a name="index-don_0027t-repeat-command"></a>
</dd>
<dt><code>dont-repeat</code></dt>
<dd><p>Used inside a user-defined command, this tells <small>GDB</small> that this
command should not be repeated when the user hits <tt class="key">RET</tt>
(see <a href="Command-Syntax.html#Command-Syntax">repeat last command</a>).
</p>
<a name="index-help-user_002ddefined"></a>
</dd>
<dt><code>help user-defined</code></dt>
<dd><p>List all user-defined commands and all python commands defined in class
COMAND_USER.  The first line of the documentation or docstring is
included (if any).
</p>
<a name="index-show-user"></a>
</dd>
<dt><code>show user</code></dt>
<dt><code>show user <var>commandname</var></code></dt>
<dd><p>Display the <small>GDB</small> commands used to define <var>commandname</var> (but
not its documentation).  If no <var>commandname</var> is given, display the
definitions for all user-defined commands.
This does not work for user-defined python commands.
</p>
<a name="index-infinite-recursion-in-user_002ddefined-commands"></a>
<a name="index-show-max_002duser_002dcall_002ddepth"></a>
<a name="index-set-max_002duser_002dcall_002ddepth"></a>
</dd>
<dt><code>show max-user-call-depth</code></dt>
<dt><code>set max-user-call-depth</code></dt>
<dd><p>The value of <code>max-user-call-depth</code> controls how many recursion
levels are allowed in user-defined commands before <small>GDB</small> suspects an
infinite recursion and aborts the command.
This does not apply to user-defined python commands.
</p></dd>
</dl>

<p>In addition to the above commands, user-defined commands frequently
use control flow commands, described in <a href="Command-Files.html#Command-Files">Command Files</a>.
</p>
<p>When user-defined commands are executed, the
commands of the definition are not printed.  An error in any command
stops execution of the user-defined command.
</p>
<p>If used interactively, commands that would ask for confirmation proceed
without asking when used inside a user-defined command.  Many <small>GDB</small>
commands that normally print messages to say what they are doing omit the
messages when used in a user-defined command.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Hooks.html#Hooks" accesskey="n" rel="next">Hooks</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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